What are the reasons Process.HasExited can throw InvalidOperationException?

I'm seeing the same message. It can happen if you do this:

System.Diagnostics.Process proc = new System.Diagnostics.Process();
proc.StartInfo.FileName = "trash filename here.exe";
try
{
    proc.Start();
}
catch { }//proc should fail.
try
{
    if (proc.HasExited)
    {
        //....
    }
}
catch (System.InvalidOperationException e)
{
    //cry and weep about it here.
}

If proc.Start() failed above, you should get to cry and weep section, too. So, if you catch after proc.Start() be sure to catch at proc.HasExited (and MANY other of the System.Diagnostics.Process Methods.

As Obalix correctly states, an InvalidOperationException is thrown when no process is attached to the Process object. This happens when a process has exited and Close or Dispose has been called on the Process object. Close releases all resources related to the process from memory. Before calling Close, this data was kept in memory to provide you (the programmer) with the information you want to know about the exited process, such as it's ExitTime and ExitCode.

The documentation states that an InvalidOperation exception is thrown in no process is associated with the object.

Have you already started the process using Process.Start() or was the process disposed before you are accessing the HasExited property?

This post also deals whith the same issue.